Spark plug



Sept. 8, 1931. E, w, STEVEN-s 1,822,462

SPARK PLUG Filed Jan. 28, 1931 gwuewcoz E. Web sEer Steven;

Patented Sept. 8, 1931 UNITED STATES ELBRIDGE WEBSTER STEVENS, OF BALTIMORE, MARYLAND SPARK PLUG Application filed January 28, 1831. Serial No. 511,883.

This invention relates to spark plugs designed for use with internal combustion engines.

The invention comprises a spark plug having as an essential element thereof a glass insulating body serving as a supporting and holding member for a center electrode, said electrode being molded or sealed in the glass and comprising a relatively inexpensive metallic tube containing a filling material -dense-.

ly packed therein.

The invention more specifically comprises a spark plug having a metallic or a conducting body providing an external shell or casing having an electrode conventionally attached thereto, a center electrode comprising an attenuated metallic tube of high conductivity, such as copper, having packed and sealed therein a refractory composition, such as magnesium oxide, the center electrode being insulated from the shell or outer casing by being embedded in a material having a high insulating value and a coefficient of expansion substantially different than the coeflicient of expansion of the metal of the center electrode; all of which is more fully hereinafter described and claimed.

One of the problems involved in the design of spark plugs for use in high compression 3o gasoline engines is that of controlling and dispelling the heat which is absorbed by the lower end of the insulator and the electrode forming its center. If this electrode, together with the lower end of the insulator, is too cool, small particles of lubricating oil and the heavy ends of liquid fuel will collect on them as condensates, which later become cracked,resultin in carbon deposit on insulator and electro e, thus interfering with proper ignition. If on the other hand, an insuificient amount of heat is dissipated from the lower end of the metallic electrode and insulator, the latter become so hot as to cause pre-ignition of the explosive mixture. These 45 temperature extremes can best be obviated by making the lower end of the insulator as short as practicable for average operating conditions, and to increase theheat transfer efliciency of the center metallic electrode and the 10 insulator so that excessive temperatures are plugs according to that patent, it was necessary. to provide a center electrode of compound wire (that is, a wire core having a sheath thereon), such compound Wire having a coefficient of expansion predetermined by the coefficients of expansion of the components thereof, that is substantially similar to the coeflicient of expansion of the glass of the insulator. While this was satisfactory generally, at times it was difficult to maintain wetted or welded seal between the metal of the electrode and the body of the glass, thus resulting in leakage to or from the combustion chamber. Furthermore, the compound wire, while presenting difliculties of accurate predetermination of its expansion coefiicient, was also relatively expensive to procure and manufacture.

'I have obviated the disadvantages and difliculties attendant upon the use of the spark plug disclosed in my prior patent by providing a new type of center electrode which not only maintains a perfect seal or weld with the glass insulator under all conditions of heating and cooling, but furthermore, is less expensive, both as to price of materials and manufacture, together with other advantages resultant upon the physical and thermal characteristics of such electrode, which shall be described hereinafter. I have provided a center electrode comprising a metallic tube such as copper having an internal core of refractory resilient elastic material, such as magnesium oxide. The metallic tube should preferably have a high heat conductivity and an electrical resistivity commensurate with its use as an electrode to provide the proper dissipation of heat and the proper sparking characteristics respectively. The refractory filler sealed and densified therein should possess an adaptability to resist fusion under heat and pressure and to have a compressibllity factor great enough to permit a variance of the mass of the metal conductor, and a coeflicient of expansion sufficient to compensate the coefficient of expansion of the metal tube. It is to be understood that depending upon the particular glass used as the insulator and the particular metal which is used as a center electrode exterior, the refractory core can be varied to suit conditions by admixing therewith either in small or large proportions one or more materials having varying coefiicients of expansion, compressibility, heat and electrical conductivities respectively. Such materials may be, for example, oxides of iron, manganese, zirconium, kieselguhr, fullers earth, oxides or compounds of calcium, silicon, aluminum, etc., or the like.-

In the prior art, it has been proposed to use magnesium oxide as a dielectric material in a spark plug, as a substitute fora brittle insulating element, such as porcelain. Such a use is shown, for example, in the United States patent to Grier, 1,560,081 of November 3, 1925. It will be seen at once that such prior proposals have no bearing on the present invention, as the use of the magnesium oxide was designed to replace and be a substitute for the porcelain insulator. In the present invention, on the, other hand, the magnesium oxide is intended to permit the use of a glass or porcelain insulator.

In the prior art, it has also been proposed to provide a porcelain insulator in a spark plug with an inner electrode formed of granular non-metallic material which is a good conductor of electricity. In my present invention, the non-metallic refractory material that I use may or may not be a conductor of electricity. The non-metallic material of my invention has a triple function-as follows:'

(1). It permits a variation in'the expansion of the insulating material and the metal embedded therein without destroying the weld or seal therebetween. This function is an attribute of the compression, and coeflicient of exapansion of the material. (2). It permits a rapid dissipation of heat from the sparking end of the electrode to the outer air when the plug is in use. This isan attribute of its heat conductivit characteristics. (3). It

permits, if desire a better electrical conductivity to assist the metal portion of the electrode. This is an attribute of its electrical resistivity. I

A preferred embodiment of my invention is shown in the accompanying drawing, but it is not limited thereto, except as hereinafter set forth in the appended claims.

The figure of the drawing shows a spark plug and its component parts in cross-section.

The insulator 1 is of glass and is held in the metal sleeve 2 by means ofthe stufling land 3, which contacts the gaskets 4 and t us prevents loss of'engine compression due to leakage. -The sleeve 2 at its innerrend has the usual threads 5 for screwing the plug in the usual opening provided for the same in the engine. The electrode 6 is attached to the metal sleeve 2 at its inner end and coacts with the center electrode 7 to produce a spark, as is well understood. The center electrode 7 is either molded, fused, welded or sealed into the glass insulator 1 and is provided at .its upper end with a binding nut 8 for proper thereto a solid metal extension 11 composed of nickel, or other like material. In making up my center electrode 7 I may proceed as follows: A hollow copper tube is densely packed with magnesium oxide so that all the air is excluded. The tube with oxide therein is the preferably swaged, forged, or attenuated (such as by wire drawing), and then the lower solid extension is attached thereto by soldering, brazing or welding. It is to be understood that although the working step is preferable in that it produces a much more compact relationship between the tube and filler, this step may be omitted without departing from my invention.

My preferred insulator is of glass, although equivalent materials may be used. Some glasses have different coeflicients of expansion than others, and an adjustment in the filler material can be made, if desired, depending upon the thermal characteristics of the metal tube and of the glass. This adjustment does not necessarily have to relate to the question of leakage between glass and electrode, as it may be desirable to make the adjustment from the standpoint of heat conductivity or even electrical resistivity. The adjustment can be made in a number of ways; for example, I have used various mixtures in the practice of my invention, such. as 80% magnesium oxide and 20% oxide of manganese; 90% magnesium oxide and 10% oxide of iron. In fact, adjustments can be made with oxides or silicates or other refractory compounds and mixtures, such as aluminum com ounds, zirconium, etc. so long as these are re ractory in nature and have fusion points above the temperature conditions of manufacture and operation'of the spark plug in service.

If my invention is followed as disclosed and described, a spark plug is produced with an insulator of fairly cheap material such glass, having embedded therein'a relatively cheap electrode which functions efficiently. Due to the presence of the filling material, the seal between the electrode and the glass is kept intact at all times without danger of leakage to or from the engine cylinder, even though the metal tube has a higher and more regular coeflicient of ex ansion than the insulator. The tube may e any desired metal such ascopper iron, nlckel or alloy material and ''preferably should have a coefiicient expansion higher than the glass or insulator used, although it may-be the same or even lower. The outer shell or casing can be varied in metallic composition and can be provided with fins'or other accessories, if desired. Claims:

1. A spark plug comprising. a metal collar, a glass insulating core, and an electrode passing'thruvthe glass comprising a copper tube having compressed anddensified therein magnesium oxide.

- 2. A spark plug comprisinga metal collar, a glass insulating core, and an electrode embedded in the glass comprising'a metal tube with a coefiicient of expansion greater than that, of said glass ,andhaving sealed within the tube a refractory material having a coeificient of expansion less than that of said glass. I

'3. A spark plug having a glass insulating. core and a central electrode comprising an attenuated copper tube containing magnesium oxide densely packed and sealed therein, and a solid extension comprising nickel welded to the lower end of said tube.

a 4. In a spark plug combination, a metal collar, a glass insulator core, and a composite electrode passing thru said glass comprising a copper tube containing an oxide of the alka-. line earth group of metals sealed in said tube. 5. A spark plug comprising a metal collar,

a glass insulating core, and an electrode embedded in the glass comprising a metal sheath containing a non-metallic filling-material, the coeflicient of expansion of the filling material 40 compensating the coeflici ent of expansion of the sheath. I I h In1 testimony whereof, I hereunto set my ELBRIDGE WEBSTER STEVENS. 

